1. Field of the Invention
An aspect of the present invention relates to an image reading apparatus, and, more particularly, to an image reading apparatus including an automatic document feeder (ADF) by which an image is read while a document is moved.
2. Description of the Related Art
Generally, an image reading apparatus reads an image printed on a document by scanning light onto the document and converting an optical signal generated from that light into an electric signal. Scanners, facsimiles, and multi-functional printers are examples of image reading apparatuses.
The image reading apparatuses include a scanning module for reading a document. The scanning module scans light onto a document to read the visible image printed on the document, converts an optical signal reflected from the document into an electrical signal, and transmits the electrical signal to a signal process module provided in the image reading apparatus.
Generally, either the scanning module or the document is moved. An image reading apparatus in which the scanning module is moved is referred to as a flat-bed type image reading apparatus. An image reading apparatus in which the document is moved is referred to as a sheet-feed type image reading apparatus. In addition, a flat-bed type image reading apparatus including an auto document feeder (ADF) is referred to as a hybrid type image reading apparatus.
The image reading apparatus includes a flat glass plane on which a document is placed and a scanning module that is disposed below the flat glass plane. The scanning module includes an optical scanning unit to scan light onto the document and an image sensor to convert an optical signal obtained by the reading of the document into an electric signal.
The optical scanning unit includes a light source that scans light from the rear surface of the flat glass plane onto the document. The light source may be a halogen lamp placed along a main scanning direction of the document. Hereinafter, a sub scanning direction indicates the direction in which a document is moved and the main scanning direction indicates the direction perpendicular to the sub-scanning direction.
The image sensor unit includes an image sensor such as a charge-coupled device (CCD) sensor or a contact image sensor (CIS) and a control board to control the operation of the image sensor.
An ADF is placed on the flat glass to move the document. The scanning module that is disposed on the rear surface of the flat glass reads an image from the document. In a mono-color image reading apparatus, the scanning module reads an image of a document based on the difference between the amounts of the light scanned and reflected from the document. The more the amount of the reflected light, the whiter the image read from the document is perceived.
Hereinafter, a margin of a document refers to the area that extends beyond the width of the document. When the width of the document is smaller in the sub-scanning direction than the length of the scanning module, the margin of the document is read as being black. This is because the light scanned onto the margin of the document is not reflected to the image sensor and instead diverges around the image sensor. A contact member is formed to prevent this effect. The contact member is elastically biased by elastic members and presses the document to closely adhere to the flat glass. In order to uniformly press the document, the elastic members should be placed at regular intervals in the main scanning direction, and the elasticity coefficient, length, and outer circumference of each of the elastic members must be substantially equal to each other. Thus, the assembly process of the image reading apparatus becomes complicated and the cost to control the quality of image scanning increases.